The present invention relates generally to balloon catheters and more specifically to balloon catheters suitable for use in stent delivery, perfusion, drug delivery, angioplasty, valvuloplasty and endartherectomy procedures. More particularly, the present invention pertains to a balloon catheter having a balloon fabricated solely of metal and to a method of making metal balloons.
It is an object of the present invention to provide a balloon catheter having a metal balloon. It is a further objective of the present invention to provide a method of making a balloon catheter having a metal balloon. The inventive metal balloon catheter consists generally of a catheter comprising a main tubular body, a metal balloon proximate a distal end of the main tubular body, a central annulus extending along an entire longitudinal aspect of the catheter for accommodating a guidewire therethrough and an inflation annulus adjacent the central annulus which extends along the longitudinal axis of the main tubular body and terminates in fluid flow communication with an inflation chamber of the metal balloon. The metal balloon catheter may consist of a unitary integral metal catheter in which the main tubular body and the balloon are fabricated of metal, or it may consist of a polymeric main tubular body and a metal balloon. As with conventional balloon catheters, the inventive metal balloon catheter has standard connectors for coupling conventional balloon catheter accessories.
The inventive metal balloon may assume a wide variety of geometries, including without limitation, tubular coils such as for use in endartherectomy procedures or as perfusion balloons, bifurcated balloons for angioplasty of vascular bifurcations or for delivery of bifurcated implantable devices, and angled balloons that have an angular offset from the longitudinal axis of the catheter. Additionally, because the inventive metal balloon is fabricated of metal, it may be made more or less radiopaque by fabricating the balloon of a radiopaque metal, such as tantalum, or providing regions on the balloon that have a radiopaque metal differentially incorporated thereupon. Moreover, the inventive metal balloon may be used either as a conductor of directly applied electrical energy or inductively energized by external application of energy, such as by ultrasound or magnetic resonance. This conductive property of the inventive metal balloon is particularly useful in diathermy, to return a signal for imaging without an added contrast medium, or return a signal to provide data concerning the in vivo environment.
The inventive metal balloon is preferably fabricated of a biocompatible metal and is formed as a film of material. The inventive metal balloon is not restricted to single layer films, but a plurality of films may be laminated to one another in order to enhance the material, geometric and/or functional properties of the resultant metal balloon. Suitable materials to fabricate the inventive metal balloon are chosen for their biocompatibility, mechanical properties, i.e., tensile strength, yield strength, and their ease of deposition, include, without limitation, the following: titanium, vanadium, aluminum, nickel, tantalum, zirconium, chromium, silver, gold, silicon, magnesium, niobium, scandium, platinum, cobalt, palladium, manganese, molybdenum and alloys thereof, such as zirconium-titanium-tantalum alloys, nitinol, and stainless steel.
The inventive metal balloon is preferably fabricated by vacuum deposition techniques. In accordance with the present invention, the preferred deposition methodologies include ion-beam assisted evaporative deposition and sputtering techniques. In ion beam-assisted evaporative deposition it is preferable to employ dual and simultaneous thermal electron beam evaporation with simultaneous ion bombardment of the substrate using an inert gas, such as argon, xenon, nitrogen or neon. Bombardment with an inert gas, such as argon ions serves to reduce void content by increasing the atomic packing density in the deposited material during deposition. The reduced void content in the deposited material is one of the important factors that allow the mechanical properties of that deposited material to be similar to the bulk material properties. Deposition rates up to 20 nm/sec are achievable using ion beam-assisted evaporative deposition techniques.
With the sputtering technique, it is preferable to employ a cylindrical sputtering target, a single circumferential source which concentrically surrounds the substrate which is held in a coaxial position within the source. Other source geometries, including spherical, are also contemplated to best coat substrates with complex geometries including the inventive balloon. Alternate deposition processes which may be employed to form the metal balloon in accordance with the present invention are cathodic arc, laser ablation, and direct ion beam deposition. When employing vacuum deposition methodologies, the crystalline structure of the deposited film affects the mechanical properties of the deposited film. These mechanical properties of the entire deposited film or differential section of the deposited film may be modified by post-process treatment, such as by, for example, annealing, high pressure treatment or gas quenching.
During deposition, the chamber pressure, the deposition pressure and the partial pressure of the process gases are controlled to optimize deposition of the desired species onto the substrate. As is known in the microelectronic fabrication, nano-fabrication and vacuum coating arts, both the reactive and non-reactive gases are controlled and the inert or non-reactive gaseous species introduced into the deposition chamber are typically argon and nitrogen. The substrate may be either stationary or moveable, either rotated about its longitudinal axis, or moved in an X-Y plane within the reactor to facilitate deposition or patterning of the deposited material onto the substrate. The deposited material maybe deposited either as a uniform solid film onto the substrate, or patterned by (a) imparting either a positive or negative pattern onto the substrate, such as by etching or photolithography techniques applied to the substrate surface to create a positive or negative image of the desired pattern or (b) using a mask or set of masks which are either stationary or moveable relative to the substrate to define the pattern applied to the substrate. Patterning may be employed to achieve regions of the metal balloon that exhibit different functional properties, such as providing folding regions that permit low profile folding of the metal balloon for endoluminal delivery, or different geometric properties of the metal balloon, such as recesses in the surface of the metal balloon having mating geometries for nesting a stent. Complex finished geometries and material properties of the resultant metal balloon, both in the context of spatial orientation of the pattern, material thicknesses at different regions of the deposited film, or differences in the crystalline structure of the metal film at different regions of the metal film may be accomplished by employing vacuum deposition techniques and post-process heat treatment of the metal film.
These and other objectives, features and advantages of the present invention will become more apparent to those of ordinary skill in the art from the following more detailed description of the present invention taken with reference to the accompanying figures.